Production of Syngas from Short-Rotation Coppice Willow
Date
2017-04-25
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
ORCID
0000-0002-1291-7866
Type
Thesis
Degree Level
Doctoral
Abstract
Bioenergy and biofuels are a low-carbon alternative to fossil fuels in Canada. Greenhouse gas emissions from sectors such as heavy transport with few non-fossil fuel alternatives can be reduced using land base renewable energy. The proliferation of coppice willow plantations is a potential reliable and effective source of biomass, particularly in the Canadian Prairies. A feedback control methodology is proposed for the development of biomass with enhanced chemical characteristics from short-rotation coppice willow. In particular, torrefaction is proposed as a pretreatment process for fluidized bed gasification, one thermochemical pathway for the production of liquid fuels and chemicals from biomass. The thesis shows that syngas quality from fluidized bed gasification of willow can be improved by torrefaction of the feedstock. Syngas quality metrics including H2/CO ratio, higher heating value of the syngas, water vapour in syngas, tar concentration and tar species concentration were used to quantify an improvement in syngas quality. The extent of torrefaction was evaluated based on the volatilization of hemicelluloses. Hemicelluloses were found to decrease linearly and significantly (p<0.05) for five torrefaction temperatures (240-280 °C). During gasification, H2/CO ratio was increased by torrefaction. The water vapour concentration in syngas was less for torrefied willow compared to non-torrefied willow. Tar concentration decreased by as much as 47 % as a result of torrefaction. The decrease in tar concentration occurred when hemicelluloses were reduced to 12 % by torrefaction. The higher heating value of the syngas, however, was lower for syngas from torrefied versus non-torrefied willow due to the increase in concentration of hydrogen in the syngas. Finally, greenhouse gas emissions were evaluated on a life-cycle basis for direct and indirect co-firing of SRC willow with lignite coal in an existing generating station in Saskatchewan. Indirect co-firing of non-torrefied willow using a circulating fluidized bed produced the largest emissions reduction. However, the indirect pathway reduced the land use efficiency of the system. Torrefied willow pellets co-fired with coal used the least land area per kWh of electricity produced. Evaluating gas composition from the torrefaction process, studying the yield of soot in syngas, and investigating the fate of alkali metals and their effect on the process are recommended extensions of this work.
Description
Keywords
Torrefaction, gasification, biomass, bioenergy, coppice willow
Citation
Degree
Doctor of Philosophy (Ph.D.)
Department
Chemical and Biological Engineering
Program
Chemical Engineering